Recently, various home appliances and electronic products have been developed in line with the technical development in electric industry and electronic industry. Most of the home appliances and the electronic products include a circuit substrate, into which an electric device, an electronic device and a semiconductor package may be inserted. The circuit substrate includes a circuit wiring for an electric connection of the electric device, the electronic device and the semiconductor package. Commonly used circuit wirings may be formed by patterning a metal layer formed on an insulating substrate. When the circuit wirings formed on the insulating substrate intersect on the same plane, a short between the circuit wirings may be generated. Thus, a common circuit substrate may include multi-layer circuit patterns electrically insulated from each other. However, a very complicated process is necessary for manufacturing the multi-layer circuit patterns on the circuit substrate, and the verification of the generation of a wiring defect during performing the manufacturing process may be difficult. Particularly, for a recently developed wafer level package, in which a circuit wiring may be directly formed on a semiconductor chip, the formation of a multi-layer circuit substrate may be very difficult because the area of the wafer level package is very small.
Meanwhile, the width of the wiring becomes narrower to form a large number of more complicated wirings on a substrate. The cross-sectional area of the wiring may be decreased according to the decrease of the width of the wiring. Thus, the resistance of the wiring may be increased, power efficiency may be decreased and heat may be generated. In order to solve the above-described defects, (1) a specific resistance (ρ) is necessary to be lowered, (2) a wiring length is necessary to be decreased, or (3) a wiring height (thickness) is necessary to be increased. With respect to method (1), the development of a material having a lower specific resistance than that of widely used copper, aluminum or silver may be difficult. With respect to method (2), practical application may be difficult concerning a circuit designing matter. With respect to method (3), the wiring may collapse, or a short between wirings may be generated in line with the increase of the height of the wiring.
Accordingly, a technique on inserting a metal wiring into a substrate is necessary. As for common methods of inserting the metal wiring into the substrate, an etching method for obtaining a desired pattern through a deposition and etching, and a damascene method of inlaying a wiring into a groove in an insulating layer by applying a copper (Cu) film, which may be hardly dry etched for forming a pattern and a CMP method, may be illustrated.
According to the above-described common methods, lots of materials may be consumed, and the process may be conducted through various steps including deposition, patterning, etching, etc. and may be complicated. In addition, since the metal layer is formed by an electroplating method, etc., a heat treatment at a high temperature may be necessary. In this case, a non-conductive material having a high temperature resistance may be required.
In Japanese Laid-open Patent Publication No. 2005-136318, a wiring substrate including a buried wiring in a transparent resin member is disclosed. Disclosed also is a method of manufacturing a wiring substrate including a wiring forming process for forming a metal wiring on a substrate, an integrating process for forming a transparent resin member by coating and drying a transparent resin solution to cover the metal wiring, and a separating process for separating the transparent resin member from the substrate. In the manufacturing method, an organic separator such as a silicon resin, a fluorine resin, etc. and an inorganic separator such as a diamond like carbon (DLC) thin film, a zirconium oxide thin film, etc. may be formed on the surface of the substrate in advance to facilitate the separating process.
However, when the inorganic separator is used, the separation of the wiring and the member may not be easily performed while conducting the separating process of the member and the metal wiring from the substrate. In this case, a portion of the metal wiring and the member may remain on the surface of the substrate, and the organic material used as the separator may stain the wiring and the surface of the member. That is, the metal wiring of the wiring substrate may be incompletely separated from the substrate even though using the separator.
The present inventors have been studied on methods of manufacturing a flexible substrate having a dented (buried) type metal wiring and completed a method of clearly separating a metal wiring and a polymer material from a substrate by treating the surface of a substrate using a plasma and then, forming the metal wiring and the polymer material (flexible substrate) on the substrate.